What is the best laptop for audio and video production on limited budget?

I'm prety much looking for the biggest bang for my buck! I would like to buy a used laptop to use for audio production and video production. Audio production is more important to be able to be done completely on (hip hop production as far as running audio program, preferably Cubase, run VSTs and other plugins smoothly for effects and instruments, and record vocals.) I would like to be able to do video production as well but more just loading videos and playback, partial editing but as far as more intensive post production can be done on pc. Platform does not matter (windows or mac). Price is more important and looking around $200 and topping out at $500. Lower the better! Battery power is my second concern and would like at least 2 hours life. Size does not matter, smaller may even be more desirable because of portability and battery life. Any suggestions? Also if possible where to get information to optimize system for audio and/or video production.